Refractory ceramic plug

ABSTRACT

The invention relates to a refractory ceramic plus for regulating a metal melt flowing past in the region of an outlet opening of a metallurgical melting vessel, for example of a tundish.

The invention relates to a refractory ceramic plug (stopper) for regulating a metal melt flowing in the region of an outlet opening of a metallurgical melting vessel, for example of a tundish.

Such a plug is usually constructed as follows: it comprises a rod-shaped body with a first end and a second end, wherein the body consists of at least one refractory ceramic material. Rod-shaped must be understood in the technical sense, i.e. the length of the body is very much greater than its diameter/its width. From the first end of the body a sacklike opening (blind hole) extends in axial direction of the body towards the second end, wherein this opening reaches as far as to a connecting region with a base and the connecting region ends in front of the second end of the body. At the first end of the body a so-called feeding region is provided since here a treatment gas more preferably an inert gas such as argon is directed into the opening of the plug. In order to direct the gas, which flows through the opening, from the region of the second end of the body into a metal melt, at least one gas channel runs from the connecting region of the opening as far as to a surface section of the body in the region of its second end. This gas channel has a cross-sectional area which is smaller than the cross-sectional area of the opening.

The plug is arranged immediately in the spout (nozzle) region of the metallurgical melting vessel, specifically in vertical orientation with the first end at the top and the second end at the bottom, adjacent to the spout. By lifting and lowering the plug a ring channel can be enlarged or reduced relative to the spout in order to regulate the quantity of the metal melt directed through/flowing past.

FIG. 1 shows such a known arrangement, wherein the plug carried the reference number 10 and a corresponding spout the reference number 50. The shown lower (second) end 14 of the plug 10 is in slightly raised position so that between plug 10 and spout 50 a ring channel is formed through which the melt S can flow from a tundish which is not shown into the spout 50 and from there into downstream installations.

The treatment gas, which is fed in via the opening 16 and from there directed into the gas channel 18 in the direction of the arrow G, which runs coaxially to the centre longitudinal axis M of the stopper-like body 10, leaves the plug 10 in the region of a spout opening 20 at the lowermost part of the second end 14 and from there it flows into the melt S.

For lifting and lowering the plug 10 it is known to fasten a metal leverage in the region of the opening 16, which with its section protruding from the plug 16 towards the top, is fastened to a corresponding lifting device.

Insofar as top and bottom are mentioned within the scope of this application, this information relates to the functioning position of the plug.

A control valve of the type shown has been used for a long time. It has however become known that in operation irregularities in the flow behavior of the melt occur from time to time.

Among other things, this is caused by the transport and feeding of the gas.

From DE 10 2005 029 033 B4 a closing plug is known wherein a filler body extends over part of the opening—viewed in axial direction of the body—wherein a gas channel extends through said filler body or between filler body and plug body—in an axial direction of said filler body—parallel to the centre longitudinal axis of the closing plug or spiral, helical or meander-like or thread-like, which connects the opening with the gas channel fluidicly, which transports the gas to the surface of the second end of the plug.

In this manner a means for adjusting the gas flow resistance is created.

It is an object of the invention to optimise a plug of the kind described to the extent that a controlled melt flow is achieved even with different positioning of the plug relative to the spout.

For solving this object, the invention is based on the following realisation:

In FIG. 2 the flow rate (m³/h) is plotted on the abscissa against the gap width between the second end (the nose) of a plug and the corresponding spout on the ordinate, specifically for a device according to FIG. 1.

The dashed line schematically characterizes the dependency in an application where no gas flows, while the closed line characterizes the dependency of the two characteristics when gas is fed in.

While there is an almost linear dependency between the opening width and the amount of melt guided through in case of no gas, a noticeably instability can be detected in case a treatment gas is fed in. In this instability region casting faults with possible defects on the end product occur.

While with low opening width in turn there is an almost linear dependency on the corresponding melt quantity, instabilities occur in the region with the dark background. This instability region in turn is followed by an almost linear curve. The flow shown to the left of the instability point is designated slug flow and the flow shown to the right of the instability point is designated bubbly flow.

It is obvious that a continuous casting plant can only be operated optimally outside the instability region shown in FIG. 2. Only then a specific change of the melt flow in terms of quantity and flow curve can be achieved by changing of the gap width.

This is where the inventive idea comes in.

A refractory ceramic plug according to the invention for regulating a metal melt flow provided the following features:

-   -   a rod-shaped body with a first end and a second end,     -   from the first end of the body a sacklike opening extends from a         feeding region in axial direction of the body as far as to a         connecting region with a base,     -   from the connecting region of the opening at least one gas         channel runs as far as to a surface section of the body in the         region of a second end,     -   the gas channel has a cross-sectional area which is smelled than         the cross-sectional area of the opening,     -   along the opening at least one section is provided through which         a gas delivered from the feeding region to the connecting region         is forcibly guided,     -   wherein said section provides an effective flow cross section         that is smaller than that of the opening,     -   in the region of the opening between the base and a section         adjacent to the base a device for measuring the gas pressure in         this region is arranged or connected thereto.

The mentioned section has a so-called restrictor function as it is fundamentally known from the already mentioned DE 10 2005 029 033 B4. While above this section there is a relatively low gas pressure, the reduced flow cross section for the gas in the region of the section leads to a clear increase of the gas pressure and the gas velocity which following this are reduced again because of an enlarged flow cross section.

Through the metal melt flow, different pressure conditions develop in the melt depending on the opening width between plug and spout, as a result of which a different vacuum acts on the fed-in gas.

With a device for measuring the gas pressure in the connecting region of the opening the exact pressure of the gas leaving the plug can be determined at any time with a plug according to the invention. Accordingly, knowing this measured pressure data, the gap width between plug and about can be adjusted so that the casting operation occurs outside the instability region as shown in FIG. 2.

This will be explained by means of an example: during casting, the regular aim is a bubbly flow. To this end, plug and spout are arranged in a suitable manner to each other as a function of the quantity and the pressure of the fed-in gas. If for example due to the operation the casting output has to be reduced or it is reduced by metallurgical influences such as clogging in an immersion pipe which follows the spout in fluid-technical respect, there is a risk that one enters the instability region and the casting quantity is increased despite a reduction of the gap width between plug and spout. This case is manifested through pressure fluctuations in the connecting region of the plug since too much gas enters the reduced melt flow. This phenomenon is now utilized for the early detection of the changed flow pattern. By reducing the gas pressure in the connecting region, the plug drops slightly in the direction of the spout, the gap width is reduced and the melt flow drops, as desired.

The device for measuring the gas pressure can be arranged directly in the mentioned region of the opening, for example as a pressure gauge, more preferably as an electronic pressure measuring device that withstands the temperatures (approx. 1500 to 1600° C.) prevailing there. Transmission of the measured pressure values to an evaluation unit can be effected via temperature-resistant cables or wireless, for example by radio.

Because of these high temperatures and the little space available in the opening region for arranging the measuring device, an alternative embodiment of the invention provides arranging a measuring channel in the region of the opening between the base and the section adjacent to the base, which connects the connecting region of the opening with a pressure measuring device. In this manner the actual pressure measuring device can also be arranged outside the plug, more preferably in a region in which less ambient temperatures prevail, i.e. for example in the region of the mentioned lifting device for lifting and lowering of the stopper. In the measuring channel, the same gas pressure as in the connecting region of the opening prevails, so that it can be measured exactly.

The measuring channel can lead from the connecting region of the opening at least in sections through the body in the direction of its first end. The measuring channel is then led out of the body for example above the melt bath and routed to the pressure measuring device via a connecting line.

The mentioned restrictor section can be embodied in different ways. One possibility is to arrange the section in the opening itself. To this end, the section can be formed by a filler body stationarily arranged in the opening, wherein at least one gas passage between the filler body and a corresponding wall of the opening remains free.

According to an alternative embodiment the section is formed by a filler body stationarily arranged in the opening, which extends over the entire cross section of the opening, wherein at least one gas passage runs through the filler body, along which a gas may flow towards the connecting region of the opening.

A further possibility of designating the section provides a filler body which extends over the entire cross section of the opening and—in axial direction—divides the opening into two regions, and a channel which connects the one region of the opening with the other region of the opening and has a cross section that is smaller than the cross section of each region of the opening. For example the channel runs through the plug body with inlet and outlet opening into the wall of the opening.

These gas passages each have a cross section that is smaller than the cross section of the opening. For example the ratio is at least 1:5 or at least 1:10, but it can also be above that. In absolute terms, the diameter may be 15 to 30 mm and that of the gas channels with reduced cross section between 2 and 7 mm.

The at least one gas channel, which leads to the surface section in the region of the second end of the body, can be an individual, discrete gas channel which for example runs co-axially to the central longitudinal axis of the plug. However, a plurality of gas channels arranged next to each other with corresponding small flow cross section each can be arranged. A further possibility is designing the so-called nose section (the second end) of the plug at least partially with a non-directed (random) porosity, i.e. that the gas does not flow in a linear manner from the opening to the plug surface as in a channel, but zig-zag like in accordance with the open porosity in this end section of the plug.

Further features of the invention are obtained from the characteristics of the subclaims as well as the other application documents.

In the following the invention is explained in more detail by means of three exemplary embodiments. There, longitudinal sections through embodiments of a plug according to the invention are each shown in schematic representation. Identical or identically acting components are explained through identical reference numbers.

The plus according to FIG. 3 comprises a refractory ceramic body 10. In axial direction of the plug, an opening 16 runs from a first end 12 as far as to a second end 14 and thus from a feeding region 22 for a treatment gas as far as to a connecting region 24 with a base 26.

From the connecting region 24 of the opening 16 a gas channel 18 runs as far as to the surface section 20 of the body 10 in the region of the second end 14. The gas channel 18 has a cross-sectional area which amounts to approximately 1/10 of the cross-sectional area of the opening 16.

Along the opening 16 a filler body 30 is provided which forms a section by which the opening 16 is sub-divided into an upper region 32 and a lower region 34. The filler body 30 extends over the entire cross-sectional area of the opening 16 and comprises a middle through-opening 36, which connects the sections 32, 34 with each other. The flow cross section of the through-opening 36 is clearly smaller than the cross section of the opening 16. The section 30 forms a type of restrictor.

The plug is embodied with a device 40 comprising a gas line 42 and a pressure gauge 44. The gas line 42 extends from a wall 38 of the region 34, then runs in the direction of the first end 12 through the body 10, in order to then leave the body 10 to the outside and continue in a gas line which leads as far as to the pressure gauge 44.

With the pressure gauge 44 the gas pressure in the region 34 of the plug, that is in the region below the filler body 30, can be continuously measured. Depending on whether the gas pressure measured in the respective application case is too high or too low a signal can be generated via a suitable computation programme in order to lift or lower the plug relative to the spout and to regulate the flow rate of the melt.

The exemplary embodiment according to FIG. 4 differs from the exemplary embodiment according to FIG. 3 in that the section (filler body) 30 completely separates the section 32 from the section 34 fluid-technically speaking. In this case the gas flows from the region 32 via a bypass 36′ within the body 10 into the region 34, wherein the flow cross section of the bypass 36′ approximately corresponds to that of the gas passage 36 in the exemplary embodiment according to FIG. 3.

In the region 34, that is between the base 26 and the section 30, a diaphragm pressure gauge 44′ is arranged, which is part of the device for determining the gas pressure in the region 34. The diaphragm pressure gauge 44′ comprises a high temperature resistant gas-permeable metal diaphragm, which bulges out differently depending on the gas pressure. The path change completed in the process is detected via a measuring line 42′ in an evaluation unit 46 and converted into corresponding gas pressure values. As described, the respective value is an indication to the steel worker to throttle or increase the flow rate of the steel melt so as not to enter the critical zone (FIG. 2).

The embodiment according to FIG. 5 fundamentally corresponds to that according to DE 10 2005 029 033 B4 with the proviso that in the region 34 which is very small in this case between section (filler body) 30 and base 26 an electronic pressure measuring device 44″ is arranged, from which a measuring line 42″ leads to an evaluation unit 46, wherein the measuring line 42″ partially extends through the body 10 of the plug.

Instead of transmission of the measurement values via cable, wireless transmission for example by radio can also be provided.

It is obvious that the pressure gauge 44 and the evaluation units 46 are arranged in a region in which preferably low temperatures prevail, i.e. outside the melt bath. 

1. A refractory ceramic plug for controlling a metal melt flow, with the following features: 1.1 A rod-shaped body (10) with a first end (12) and a second end (14), 1.2 From the first end (12) of the body (10) a sack-like opening (16) extends from a feeding region (22) in axial direction of the body (10) as far as to a connecting region (24) with a base (26), 1.3 From the connecting region (24) of the opening (16) at least one gas channel (18) runs as far as to a surface section (20) of the body (10) in the region of its second end (14), 1.4 The gas channel (18) has a cross-sectional area that is smaller than the cross-sectional area of the opening (16), 1.5 Along the opening (16) at least one section (30) is provided through which a gas delivered from the feeding region (22) to the connecting region (24) is forcibly fed, wherein the section (30) has an effective flow cross section that is smaller than that of the opening (16), 1.6 In the region of the opening (16) between the base (26) and the section (30) adjacent to the base (26) a device (40) for measuring the gas pressure in this region (34) is arranged or connected thereto.
 2. The plug according to claim 1, with a gas channel (18) running coaxially to the opening (16).
 3. The plug according to claim 1 whose section (30) lies with the opening (16).
 4. The plug according to claim 1, whose section (30) is formed by a filler body stationarily arranged in the opening (16), wherein at least one gas passage between the filler body and a corresponding wall (38) of the opening (16) remains free.
 5. The plug according to claim 1, whose section (30) is formed by a filler body stationarily arranged in the opening (16), which extends over the entire cross section of the opening (16) wherein at least one gas passage (36) runs through the filler body, through which a gas flows in the direction of the connecting region (24) of the opening (16).
 6. The plug according to claim 1, with a filler body (30) which extends over the entire cross section of the opening (16) and divides the opening (16) in axial direction into two regions (32, 34), and with a channel (36′), which connects the one region (32) of the opening (16) with the other region (34) of the opening (16) and has a cross section that is smaller than the cross section of each region (32, 34) of the opening (16).
 7. The plug according to claim 1, whose device (40) for the measurement of the gas pressure comprises a pressure gauge (44).
 8. The plug according to claim 1, whose device (40) for the measurement of the gas pressure comprises a measuring channel (42) which connects the connecting region (34) of the opening (16) with a pressure measuring device (44).
 9. The plug according to claim 8, whose measuring channel (42) leads from the connecting region (34) at least in sections through the body (10) in the direction of its first end (12).
 10. The plug according to claim 1, whose device (40) for the measurement of the gas pressure comprises a pressure measuring device (44′, 44″) arranged in the connecting region (34).
 11. The plug according to claim 1, whose device (40) for the measurement of the gas pressure comprises a diaphragm pressure gauge (44′).
 12. The plug according to claim 1, whose device (40) for the measurement of the gas pressure comprises an electronic pressure measuring device (44″). 